It is known that different substrates absorb different, specific bands of IR (infrared) radiation. Thus, by directing IR radiation towards a thin film of the substrate it is possible to determine the thickness of the film. By a radiometric analysis it is further possible to determine the proportion of ingredients in the substrate and by continuous monitoring it is possible to establish changes of said proportion. Radiometric analysis is based on the change of energy or absorption of radiation, which in this case has wave-lengths within the IR area.
In many applications it is important to be able to control the thickness of a fluid film and the amount of different ingredients of the fluid film. This control could be used to optimize the desired effect, reduce the amount of used fluid and thereby save costs. In many instances it is normal to use superfluous amounts of a fluid, to be on the safe side. Controlling and monitoring the actual amount of fluid and its ingredients may diminish such superfluous amounts.